Methods for fabricating shapes by use of organometallic ceramic precursor binders

ABSTRACT

This invention relates to the discovery of organometallic ceramic precursor binders used to fabricate shaped bodies by different techniques. Exemplary shape making techniques which utilize hardenable, liquid, organometallic, ceramic precursor binders include the fabrication of negatives of parts to be made (e.g., sand molds and sand cores for metalcasting, etc.), as well as utilizing ceramic precursor binders to make shapes directly (e.g., brake shoes, brake pads, clutch parts, grinding wheels, polymer concrete, refractory patches and liners, etc.). In a preferred embodiment, this invention relates to thermosettable, liquid ceramic precursors which provide suitable-strength sand molds sand cores at very low binder levels and which, upon exposure to molten metalcasting exhibit low emissions toxicity as a result of their high char yields of ceramic upon exposure to heat.

This application is a 371 of PCT/US94/04806, filed 28 Apr., 1994, whichis a CIP of 08/055,654, filed 30 Apr., 1993, now abandoned.

TECHNICAL FIELD

This invention relates to the discovery of organometallic ceramicprecursor binders used to fabricate shaped bodies by differenttechniques. Exemplary shape making techniques which utilize hardenable,liquid, organometallic, ceramic precursor binders include thefabrication of negatives of parts to be made (e.g., sand molds and sandcores for metalcasting, etc.), as well as utilizing ceramic precursorbinders to make shapes directly (e.g., brake shoes, brake pads, clutchparts, grinding wheels, polymer concrete, refractory patches and liners,etc.). In a preferred embodiment, this invention relates tothermosettable, liquid ceramic precursors which providesuitable-strength sand molds and sand cores at very low binder levelsand which, upon exposure to molten metalcasting exhibit low emissionstoxicity as a result of their high char yields of ceramic upon exposureto heat.

BACKGROUND ART

The casting of metal articles using sand molds, sand shells and sandcores is well known in the art. Detailed information regarding the stateof this technology can be found, for example, in a text by James P.LaRue, EdD, Basic Metalcasting, (The American Foundrymen's Society,Inc., Des Plaines, Ill., 1989, the subject matter of which is hereinincorporated by reference). Using such a technique, a mold can be madefrom a mixture of sand and (typically) an organic binder by packing themixture loosely or tightly around a pattern. The pattern is thenremoved, leaving a cavity in the sand which replicates the shape of thepattern. Once the organic binder is shape-stabilized by any of a numberof hardening techniques (as described below), the cavities in the sandmold are filled with molten metal by pouring the molten metal into themold.

In a typical shell molding operation, binder-coated sand can be blownonto the interior surface of a heated metal pattern. In a relativelyshort time (20-30 seconds) the heat from the pattern penetrates thesand, producing a bond in the heat-affected layer. This layer clings tothe pattern, and when the pattern is rotated, the sand not affected bythe heat falls into a hopper for further use. The thin, bonded layer ofbinder-coated sand clinging to the pattern is then cured by heating. Thecured shell is then pushed from the pattern by ejector pins. When amating shell is produced, the shells are aligned and fastened togetherwith a high-temperature adhesive for pouring.

Just as the sand mold cavity provides the external shape of a casting,any holes or other internal shapes in a casting can be produced by usingsand cores. When such cores are made from sand, numerous acceptableprocesses for making these cores are acceptable. In most cases, a sandmixture comprising a binder material is placed into a corebox. There,the sand mixture takes the shape of the cavity in the box, becomes hard,and is removed. After the mold is made, the core is then set in the"drag" just before the mold is closed. When the metal is poured, themolten metal fills the mold cavity except for where sand cores arepresent. Thus, the shape of the solidified casting results from thecombined shapes of the mold and the sand core(s).

Before 1943, coremaking was simple. There was one core process, known asoil-sand, which had been used for many years. Since then, there has beena dramatic increase in coremaking technology. At present there are atleast 21 different coremaking systems. Over 160 binder materials are nowavailable for making cores. These binder materials can be categorized asvapor-cured (cured by a gas of some kind), heat-cured (cured by heat),or no-bake (cured by chemical reaction).

While it is not the intent of this disclosure to discuss all of thevarious binders which are currently in use for such processes, perhapsthe most commonly utilized binders comprise both inorganic and organicresins.

In the realm of inorganic systems, both vapor-cured and no-bake sodiumsilicate binders are known. No-bake, oxide-cured phosphate binders arealso available. Such inorganic binders often have low emissionsresulting from their high char forming characteristics. The term "char"should be understood as meaning the solid products of binderdecomposition which remain after thermal treatment during themetalcasting process. They do, however, have certain disadvantages.

Vapor-cured sodium silicate binders, for example, are typicallyprocessed by coating sand grains with the sodium silicate binder,backing the mixture into a corebox, and then gassing the mixture in thecorebox with carbon dioxide for a short period of time (about 10seconds). This treatment hardens the core, allowing it to be removedfrom the corebox. One advantage of this system is that the core can beused immediately. A major disadvantage of such systems, however, is thetendency for the resulting cores to absorb moisture. Many of theinorganic resin systems currently in use share this problem.

By far, the largest number of sand binders which are used in the art ofmetalcasting are organic resins. Vapor-cured systems include thephenolic urethane/amine binders, phenolic esters, furan/peroxide systemswhich, typically, are acid cured, and epoxy/sulfur dioxide systems.Heat-cured systems include phenolic resins, furan systems, and ureaformaldehyde binders. No-bake systems comprise acid-cured furan systems,acid-cured phenolic resins, alkyd oil urethanes, phenolic urethanes, andphenolic esters. While these wholly organic systems often offerflexibility in processing (e.g., these systems can be solvent processed,melted, etc.), the hardened molds or cores produced using such bindershave very serious drawbacks including, for example, the evolution oftoxic emissions during the metal casting process due to the low charyield characteristics of organic resins.

Organometallic, ceramic precursors are known in the art of ceramicprocessing. These materials can be in the form of either solvent-solublesolids, meltable solids, or hardenable liquids, all of which permit theprocessibility of their organic counterparts in the fabrication ofceramic "green bodies". During the sintering of such green parts,however, the ceramic precursor binders have the added advantage ofcontributing to the overall ceramic content of the finished part,because the thermal decomposition of such ceramic precursor bindersresults in relatively high yields of ceramic "char". Thus, most of theprecursor is retained in the finished part as ceramic material, and verylittle mass is evolved as undesirable volatiles. This second feature isadvantageous, for example, in reducing part shrinkage and the amount ofvoids present in the fired part, thereby reducing the number ofcritically sized flaws which have been shown to result in strengthdegradation of formed bodies.

Such precursors can be monomeric, oligomeric, or polymeric and can becharacterized generally by their processing flexibility and high charyields of ceramic material upon thermal decomposition (i.e. pyrolysis).These precursors are neither wholly inorganic nor wholly organicmaterials, since they comprise metal-carbon bonds. These precursors canbe distinguished from other known inorganic binders for sand moldfabrication described above (which comprise no carbon), and other knownorganic binders (which comprise no metallic elements). It has beenunexpectedly discovered that such organometallic "hybrids" which arehardenable liquids are uniquely suited for use as binders for sandgrains in the fabrication of sand molds, cores, and shells, since theycan provide excellent mold strength at extremely low binder levels.Their utility resides in a unique combination of, for example, theprocessing flexibility afforded by organic binders and the high charforming characteristics and improved adhesion to sand of inorganicbinders. Such binders can therefore be easily processed to provide ahardened sand mold, and subsequently used for metalcasting with aminimum of toxic volatiles being evolved. Additionally, when suchbinders are used to bond particles together to make shapes directly,similar problems to those discussed above also result. For example,similar problems can occur when making brake shoes, brake pads, clutchparts, gravity wheels, polymer concrete, refractory patches and liners,etc. Since such binders are also liquids, they can be employed directlywithout use of a solvent. This obviates the emissions and disposalproblems associated with solvent-based systems which require a "drying"step subsequent to mold shaping.

Siloxanes have been used in the past to improve the adhesion of suchbinder systems as polycyanoacrylates to sand grains (see, for example,U.S. Pat. No. 4,076,685). In such a system the siloxane is used as aprocessing aid rather than the binder itself. Additionally, partialcondensates of trisilanols have been used in combination with silica asbinder systems which are provided in aliphatic alcohol-water cosolvent(see, for example, U.S. Pat. No. 3,898,090). Such in-solvent bindershave been shown to suffer the disadvantage of short shelf life ("severaldays") due to additional silanol condensation during storage. A furtherdisadvantage is that these binders require the step of solvent removalfrom the core or mold by a drying process ("to remove a major portion ofthe alcohol-water cosolvent") before metalcasting. Otherwise, voids andpoor mold integrity result during the metalcasting process. The use ofhardenable, liquid organometallic, ceramic precursors as solventlessbinders for the fabrication of sand molds, shells, and cores has notbeen disclosed. FR-A-1365207 discloses the use of an organometallicbinder in the fabrication of refractory objects. Specifically, thebinders are liquid, based on organic compounds of titanium, and hardenedby a process of hydrolysis.

DESCRIPTION OF COMMONLY OWNED U.S. PATENTS AND PATENT APPLICATIONS

This application is a continuation-in-part of commonly owned andcopending U.S. patent application Ser. No. 08/055,654, filed Apr. 30,1993, in the names of Jonathan W. Hinton et al., and entitled "Methodsfor Fabricating Shapes by Use of Organometallic Ceramic PrecursorBinders", now abandoned.

SUMMARY OF THE INVENTION

This invention relates to the discovery of organometallic ceramicprecursor binders used to fabricate shaped bodies by differenttechniques. Exemplary shape making techniques which utilize hardenable,liquid, organometallic, ceramic precursor binders include thefabrication of negatives of parts to be made (e.g., sand molds and sandcores for metalcasting, etc.), as well as utilizing ceramic precursorbinders to make shapes directly (e.g., brake shoes, brake pads, clutchparts, grinding wheels, polymer concrete, refractory patches and liners,etc.).

A preferred embodiment of the invention relates to the fabrication ofshaped metal, or metal matrix composite, articles by metalcasting intosand molds, shells or sand cores prepared using hardenable, liquid,organometallic, ceramic precursor binders. In this preferred embodiment,the method comprises (1) solventless coating of the surface of sand witha hardenable, liquid, organometallic, ceramic precursor binder, (2)forming a shape from said sand/binder mixture, (3) hardening said binderto form a sand mold, shell, or core, and (4) metalcasting into theresulting hardened sand mold, shell, or core to form a shaped metalarticle.

It has been discovered that such solventless binder compositions can beused at very low binder levels since (1) such binders can be made to beliquids and provide for excellent sand grain surface wetting, and (2)the binders are provided without solvent. Surprisingly, binder levels aslow as 0.1 wt % of a polyureasilazane comprising crosslinkable vinylgroups result in sand molds which have excellent strength inmetalcasting operations.

In a typical process according to a preferred embodiment of theinvention, a predetermined quantity of sand (e.g., silica sand such asunbonded sand, washed sand, crude sand, lake sand, bank sand andnaturally bonded sand; zircon sand; olivine sand; magnesite sand;chromite sand; hevi-sand; chromite-spinel sand; carbon sand; siliconcarbide sand; chamotte sand; mullite sand; kyanite sand; sillimanitesand; alumina sand; corundum sand; etc., and combinations and mixturesthereof) is coated by mixing the sand with an organometallic, ceramicprecursor binder in an amount sufficient to result in a hardened sandmold, shell, or core having suitable strength for ease of handling, aswell as sufficient structural integrity needed for the metalcastingprocess. However, the aforementioned sufficient strength should not betoo great so as to deleteriously impact the ability to remove a castmetal part from a sand mold (e.g., by physically breaking the sand moldaway from the cast part).

The sand/binder mixture is then shaped using standard procedures forpreparing metalcasting molds, shells, or cores and then hardened using aprocedure suited to the exact chemical composition of theorganometallic, ceramic precursor binder.

The hardened mold, shell, or core is then used to pour a shaped metalobject by a metalcasting process. It should be understood that whilethis disclosure refers primarily to a metalcasting process, the conceptsof this disclosure also apply to the casting of metal matrix compositearticles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a photograph of the cast aluminum alloy piece and the sandmold formed in Example 5.

FIG. 2 is a photograph of the cast iron piece and the sand mold formedin Example 7.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

This invention relates to the discovery of organometallic ceramicprecursor binders used to fabricate shaped bodies by differenttechniques. Exemplary shape making techniques which utilize hardenable,liquid, organometallic, ceramic precursor binders include thefabrication of negatives of parts to be made (e.g., sand molds and sandcores for metalcasting, etc.), as well as utilizing ceramic precursorbinders to make shapes directly (e.g., brake shoes, brake pads, clutchparts, grinding wheels, polymer concrete, refractory patches and liners,etc.).

The organometallic, ceramic precursor binders suitable for the practiceof this invention include monomers, oligomers and polymers. The term"organometallic" should be understood as meaning a compositioncomprising a metal-carbon bond. Suitable metals include both main groupand transition metals selected from the group consisting of metals andmetalloids selected from IUPAC groups 1 through 15 of the periodic tableof elements inclusive. Preferred metals/metalloids include titanium,zirconium, silicon and aluminum, with silicon being a preferredselection.

While monomeric ceramic precursors can satisfy the requirementsnecessary for the practice of this invention, monomers that polymerizeto form hard polymers of appreciable ceramic yield (e.g., greater than20 percent by weight) often have so low a molecular weight thatvolatilization at modest molding temperatures becomes a problem. Oneexample of this is vinyltrimethylsilane, which has a boiling point ofonly 55° C. Curing this monomer by thermal or radical means to form ahardened binder requires temperatures greater than the boiling point ofthe monomer. It is thus unsuitable in the process described. Becausemonomers are generally too volatile to be used in this molding process,the preferred liquid ceramic precursors of this invention are eitheroligomeric or polymeric. An oligomer is defined as a polymer moleculeconsisting of only a few monomer repeat units (e.g., greater than twoand generally less than 30) while a polymer has monomer repeat units inexcess of 30. Suitable polymers include, for example, but should not beconstrued as being limited to polysilazanes, polyureasilazanes,polythioureasilazanes, polycarbosilanes, polysilanes, and polysiloxanes.Precursors to oxide ceramics such as aluminum oxide as well as non-oxideceramics can also be used. Organometallic, ceramic precursors suitablefor the practice of this invention should have char yields in excess of20 percent by weight, preferably in excess of 40 percent by weight, andmore preferably in excess of 50 percent by weight when the hardenedprecursor is thermally decomposed.

The organometallic, ceramic precursors suitable for the practice of thisinvention preferably contain sites of organounsaturation such asalkenyl, alkynyl, epoxy, acrylate or methacrylate groups. Such groupsmay facilitate hardening when energy in the form of heat, UVirradiation, or laser energy is provided to promote a free radical orionic crosslinking mechanism of the organounsaturated groups. Suchcrosslinking reactions promote rapid hardening and result in hardenedbinders having higher ceramic yields upon pyrolysis. High ceramic yieldtypically results in lower volatiles evolution during metalcasting.Specific examples of such precursors includepoly(acryloxypropylmethyl)siloxane,glycidoxypropylmethyldimethylsiloxane copolymer,polyvinylmethylsiloxane, poly(methylvinyl)silazane,1,2,5-trimethyl-1,3,5-trivinyltrisilazane,1,3,5,7-tetramethyl-1,3,5,7-tetravinyltetrasilazane,1,3,5-tetravinyltetramethylcyclotetrasiloxane,tris(vinyldimethylsiloxy)methylsilane, and trivinylmethylsilane.

When heat is provided as the source of energy, a free radical generator,such as a peroxide or azo compound, may, optionally, be added to promoterapid hardening at a low temperature.

Exemplary peroxides for use in the present invention include, forexample, diaroyl peroxides such as dibenzoyl peroxide, dip-chlorobenzoyl peroxide, and bis-2,4-dichlorobenzoyl peroxide; dialkylperoxides such as 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and dit-butyl peroxide; diaralkyl peroxides such as dicumyl peroxide; alkylaralkyl peroxides such as t-butyl cumyl peroxide and1,4-bis(t-butylperoxyisopropyl)benzene; alkylaroyl peroxides andalkylacyl peroxides such as t-butyl perbenzoate, t-butyl peracetate, andt-butyl peroctoate. It is also possible to use peroxysiloxanes asdescribed, for example, in U.S. Pat. No. 2,970,982 (the subject matterof which is herein incorporated by reference) and peroxycarbonates suchas t-butylperoxy isopropyl carbonate.

Symmetrical or unsymmetrical azo compounds, such as the following, maybe used as free radical generators: 2,2'-azobis(2-methylpropionitrile);2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile);1-cyano-1-(t-butylazo)cyclohexane; and 2-(t-butylazo)isobutyronitrile.These products are well known and are described, for example, in U.S.Pat. Nos. 2,492,763 and 2,515,628 (the subject matter of which is hereinincorporated by reference).

In addition to crosslinking which may be provided through sites oforganounsaturation which are appended to the organometallic, ceramicprecursor binder, additional modes of crosslinking provided by polymerchain condensation upon pyrolysis may be beneficial. Thus, for example,silicon polymers comprising nitrogen are preferred to silicon polymerscomprising oxygen, since nitrogen is trivalent. In polysilazanes, forinstance, the repeat unit of the polymer chain contains Si--N bonds inwhich the nitrogen atom is then further bonded both to either twoaddition silicon atoms, or a silicon atom and a carbon or hydrogen atom.Upon thermal treatment, such polysilazanes crosslink via N--C or N--Hbond cleavage with subsequent crosslinking provided by formation of anadditional Si--N bond. Such crosslinking provides for higher char yieldsupon binder hardening. This leads to lower volatiles evolution duringmetalcasting when such polymers are used as binders for the sand mold,shells, or cores which are used.

Known methods for coating the sand with the liquid, organometallic,ceramic precursor may be used, including, but are not limited to simplehand mixing, mulling, milling, etc. Typical sands suitable for suchapplication include, but are not limited to silica sand such as unbondedsand, washed sand, crude sand, lake sand, bank sand and naturally bondedsand, zircon sand; olivine sand; magnesite sand; chromite sand;hevi-sand; chromite-spinel sand; carbon sand; silicon carbide sand;chamotte sand; mullite sand; kyanite sand; sillimonate sand; aluminumsand; corundum sand; etc.; and combinations and mixtures thereof.

The amount of organometallic, ceramic precursor binder used in coatingshould be such that the strength of the hardened, molded sand object issufficient to provide for easy handling and also sufficient to ensurestructural integrity of the mold during the metalcasting process.Surprisingly, when suitable organometallic ceramic precursors are usedsuch binder levels can be quite low. While binder levels can be in therange of 0.1% to about 20% based on the total weight of the sand/bindermixture, preferably 0.1 wt % to 5 wt %, and more preferably 0.1 wt % to2 wt % of binder should be used. When highly crosslinkableorganometallic, ceramic precursor binders are used, the lowest levels ofbinder can be achieved.

While not wishing to be bound by any particular theory or explanation,it is believed that the unique suitability of such organic/inorganic"hybrid" systems derives from their ability to provide the processingflexibility and hardened strength of organic resin binders with the sandsurface-compatibility of inorganic binder systems. Such sandsurface-compatibility is described in, for example, U.S. Pat. No.4,076,685 (the subject matter of which is herein incorporated byreference), wherein a siloxane is used to promote adhesion of athermoplastic cyanoacrylate polymer binder to sand grains.

Once formulated, the sand/binder mixture can be formed into molds,shells, or cores by any technique known in the art. Binder hardening isthen accomplished by vapor arc, heat arc, chemical cure and/orcombinations thereof.

In a preferred embodiment, the organometallic ceramic precursor bindercomprises a site of organounsaturation such as a vinyl group which canbe crosslinked by thermal treatment to harden the binder. When suchcompositions are used, a free radical initiator can be added to thecomposition to facilitate the free radical crosslinking of the binderwhich serves to harden irreversibly the composition. When a free radicalgenerator is used, a temperature is generally selected so that thehardening time is greater or equal to one or preferably two half livesof the initiator at that temperature. It is important for thesand/binder mixture to harden sufficiently so that ease of handling andmetalcasting can be ensured. Suitable free radical initiators include,but are not limited to, organic peroxides, inorganic peroxides, and azocompounds.

Once the binder is hardened, the sand molds, shells, and cores can thenbe used for metalcasting. Typical metals suitable for casting includealuminum, aluminum alloys, iron, ferrous alloys, copper, copper alloys,magnesium, magnesium alloys, nickel, nickel alloys, corrosion and heatresistant steels, zinc, zinc alloys, titanium, titanium alloys, cobalt,cobalt alloys, silicon bronzes, brass, tin bronzes, manganese bronzes,stainless steels, high alloy steels, vanadium, vanadium alloy,manganese, manganese alloys, zirconium, zirconium alloys, columbium,columbium alloys, silver, silver alloys, cadmium, cadmium alloys,indium, indium alloys, hafnium, hafnium alloys, gold, gold alloys, etc.,and composites including such metals as the matrix.

The following non-limiting examples are provided to illustrate the useof polysilazane and polysiloxane ceramic precursor binders in thepreparation of sand molds and sand cores for the metalcasting ofaluminum/silicon alloy and iron.

EXAMPLE 1

This Example demonstrates, among other things, a method for fabricatinga sand mold for metalcasting using a polyureasilazane in accordance withthe present invention.

An about 8.0 gram sample of a polyureasilazane prepared as described inU.S. Pat. No. 4,929,704 (which is herein incorporated in its entirety byreference), Example 4, was combined with about 5.0 percent by weightdicumyl peroxide. Washed silica sand (about 192 gram, Wedron Silica Co.,Wedron, Ill.) was hand mixed into the polymer/peroxide blend to give a"wet" sand consistency with a polymer loading level of about 4 weightpercent. An about 20 gram sample of the polymer/sand mixture was loadedinto a conically shaped crucible and compacted. The crucible was heatedto about 120° C. for a period of about 1 hour, the temperature wasraised to about 130° C. and the crucible was held at this temperaturefor about 1 hour, and the temperature was then raised to about 140° C.for about 0.5 hour. The vessel was allowed to cool to room temperature.The polymer/sand mixture had hardened in the crucible, and replicatedthe exact shape of the crucible. The molded piece could be sanded to anew shape by rubbing with coarse silicon carbide abrasive cloth. Thehardened 4 percent by weight part could be dropped or thrown against atable top without visible damage.

EXAMPLE 2

This Example demonstrates, among other things, the use of differingbinder amounts in a sand mold fabricated in accordance with the presentinvention.

In the same manner as Example 1, polymer sand mixtures were prepared atthe 0.5 percent by weight and 1 percent by weight polymer levels. About20 gram samples were loaded into crucibles and cured according to theheating schedule of Example 1. The following observations were noted.The cured 1.0 percent by weight part could be dropped or thrown onto thetable top with only slight visible edge damage. The 0.5 percent byweight cured part could be crumbled by hand using considerable effort.

EXAMPLE 3

This Example demonstrates, among other things, a method for fabricatinga sand mold for metalcasting using a polysilazane in accordance with thepresent invention. Substantially the same procedure used in Example 1was used to prepare a hardened part comprising 4 percent by weightpoly(methylvinyl)silazane binder prepared by the ammonolysis of an 80:20molar ratio mixture of methyldichlorosilane to vinylmethyldichlorosilanein hexane solvent according to procedures detailed in Example 1 of U.S.Pat. No. 4,929,704. The part could be dropped or thrown against a tabletop without visible damage.

EXAMPLE 4

This Example demonstrates, among other things, a method for fabricatinga sand mold for metal casting in accordance with the present invention.

Dicumyl peroxide (about 1.2 gram) was dissolved in the polyureasilazanepolymer described in Example 1 (about 24 grams). Washed silica sand(about 1176 grams, Wedron Silica Co., Wedron, ILL.) was slowly mixedinto the polymer/peroxide blend to form an about 2 percent by weightpolymer/sand mixture. This 2 percent by weight binder/sand mixture waspacked into a rubber mold containing a positive definition well formetal casting. The binder/sand mixture was cured in an air atmosphereoven at about 100° C. for a period of about 30 minutes, the temperaturewas raised to about 110° C. for about 1 hour, and then raised to about125° C. for about 1 hour. The mold was cooled to room temperature andthe sand was demolded. The sand replicated the shape of the mold.

EXAMPLE 5

This Example demonstrates, among other things, a method for fabricatinga sand mold for metal casting and thereafter casting molten aluminumalloy into the cavity of the sand mold.

Dicumyl peroxide (about 0.6 gram) was dissolved in the polyureasilazanepolymer described in Example 1 (about 12 grams). Washed silica sand(about 1176 grams, Wedron Silica Co., Wedron, Ill.) was slowly mixedinto the polymer/peroxide blend to form a 1 percent by weightpolymer/sand mixture. This 1 percent by weight binder/sand mixture waspacked into a rubber mold containing a positive definition well formetal casting. The binder/sand mixture was cured in an air atmosphereoven at about 100° C. for a period of about 30 minutes, the temperaturewas raised to about 110° C. for about 1 hour, and then raised to about125° C. for about 1 hour. The mold was cooled to room temperature andthe sand was demolded. The sand replicated the shape of the mold.

The cured mold was then placed on a table and an aluminum alloycomprising about 10% silicon by weight, balance aluminum, was melted andraised to a temperature of about 700° C. After stabilizing thetemperature of the molten aluminum alloy at about 700° C., a ladle wasdipped into the molten aluminum alloy and a small sample of the aluminumalloy was slowly poured into the cavity of the mold and the aluminumalloy was allowed to cool to room temperature.

FIG. 1 is a photograph of the cast aluminum alloy part and the mold.

EXAMPLE 6

This Example demonstrates, among other things, a method for fabricatinga sand mold for metal casting and thereafter casting molten aluminumalloy around the sand mold.

Dicumyl peroxide (about 1.2 gram) was dissolved in the polyureasilazanepolymer described in Example 1 (about 24 grams). Washed silica sand(about 1176 grams, Wedron Silica Co., Wedron, Ill.) was slowly mixedinto the polymer/peroxide blend to form a 2 percent by weightpolymer/sand mixture. This 2 percent by weight binder/sand mixture waspacked into a rubber mold containing a positive definition well formetal casting. The binder/sand mixture was cured in an air atmosphereoven at about 100° C. for a period of about 30 minutes, the temperaturewas raised to about 110° C. for about 1 hour, and then raised to about125° C. for about 1 hour. The mold was cooled to room temperature andthe sand was demolded. The sand replicated the shape of the mold.

The cured sand mold was placed into a graphite mold having a cavitymeasuring about 7 inches by 7 inches by 1 inch (178 mm by 178 mm by 25mm). An aluminum alloy comprising about 10% by weight silicon, balancealuminum, was melted and maintained at a temperature of about 700° C. Aladle was dipped into the molten aluminum and a small sample of thealuminum alloy was poured into the graphite mold, around the cured sandmold, but not into its cavity, and allowed to cool to room temperature.

EXAMPLE 7

This Example demonstrates, among other things, a method for fabricatinga sand mold for metal casting and thereafter casting molten cast ironinto the cavity of the sand mold.

Dicumyl peroxide (about 0.6 gram) was dissolved in the polyureasilazanepolymer described in Example 1 (about 12 grams). Washed silica sand(about 1176 grams, Wedron Silica Co., Wedron, Ill.) was slowly mixedinto the polymer/peroxide blend to form a 1 percent by weightpolymer/sand mixture. This 1 percent by weight binder/sand mixture waspacked into a rubber mold containing a positive definition well formetal casting. The binder/sand mixture was cured in an air atmosphereoven at about 100° C. for a period of about 30 minutes, the temperaturewas raised to about 110° C. for about 1 hour, and then raised to about125° C. for about 1 hour. The mold was cooled to room temperature andthe sand was demolded. The sand replicated the shape of the mold.

A quantity of cast iron was placed into a small crucible and melted andmaintained at a temperature of about 1350° C. After maintaining atemperature of about 1350° C., a small amount of the cast iron waspoured from the crucible into the center cavity of the cured sand moldand allowed to cool to room temperature. FIG. 2 is a photograph of thecooled cast iron piece and the sand mold.

EXAMPLE 8

This Example demonstrates, among other things, a method for fabricatinga sand mold for metal casting and thereafter casting molten cast ironaround the sand mold.

Dicumyl peroxide (about 1.2 grams) was dissolved in the polyureasilazanepolymer described in Example 1 (about 24 grams). Washed silica sand(about 1176 grams, Wedron Silica Co., Wedron, Ill.) was slowly mixedinto the polymer/peroxide blend to form a 2 percent by weightpolymer/sand mixture. This 2 percent by weight binder/sand mixture waspacked into a rubber mold containing a positive definition well formetal casting. The binder/sand mixture was cured in an air atmosphereoven at about 100° C. for a period of about 30 minutes, the temperaturewas raised to about 110° C. for about 1 hour, and then raised to about125° C. for about 1 hour. The mold was cooled to room temperature andthe sand was demolded. The sand replicated the shape of the mold.

The cured sand piece was placed into a steel frame having a cavity ofabout 6 inches by 5 inches (152 mm by 127 mm). A quantity of cast ironwas melted in a small crucible and maintained at a temperature of about1350° C. The cast iron was then poured from the crucible into the steelframe and around the cured sand piece, but not into its cavity, andallowed to cool to room temperature.

We claim:
 1. A process for fabricating shaped articles by castingcomprising:at least partially coating the surface of at least one sandwith at least one hardenable, solventless liquid, organometallic,ceramic precursor binder comprising a material selected from the groupconsisting of polysilazane, polyureasilazane, polythioureasilazane andpolysiloxane to form a sand/binder mixture; forming at least one shapefrom said sand/binder mixture; hardening said sand/binder mixture by acrosslinking mechanism to form at least one sand mold, shell, or core;and casting at least one metal or metal matrix composite into theresulting hardened at least one sand mold, shell, or core to form atleast one shaped metal or metal matrix composite article.
 2. Asand/binder mixture comprising (1) at least one sand and (2) at leastone at least one hardenable, solventless liquid, organometallic, ceramicprecursor binder, said binder comprising at least one metal-carbon bond,at least partially coated on the surface of said at least one sandcharacterized in that said sand/binder mixture is hardenable by acrosslinking mechanism.
 3. The sand/binder mixture of claim 2, whereinsaid at least one hardenable, liquid, organometallic, ceramic precursorbinder comprises at least one composition selected from the groupconsisting of polysilazane, polyureasilazane, polythioureasilazane, andpolysiloxane.
 4. A process for fabricating shaped articles by casting,said process comprising (1) at least partially coating the surface of atleast one sand with at least one hardenable, solventless liquid,organometallic ceramic precursor binder, said binder comprising at leastone metal-carbon bond, to form a sand/binder mixture, (2) forming atleast one shape from said sand/binder mixture, characterized byhardening said sand/binder mixture by a crosslinking mechanism to format least one sand mold, shell, or core, and (3) casting at least onemetal or metal matrix composite into the resulting hardened at least onesand mold, shell, or core to form at least one shaped metal or metalmatrix composite article.
 5. The process of claim 4, wherein said atleast one sand comprises at least one of silica sand, zircon sand,olivine sand, magnesite sand, chromite sand, hevi-sand, chromite-spinelsand, carbon sand, unbonded sand, washed sand, crude sand, lake sand,bank sand, naturally bonded sand, silicon carbide sand, chamotte sand,mullite sand, kyanite sand, sillimonate sand, aluminum sand, corundumsand, and combinations and mixtures thereof.
 6. The process of claim 4,wherein said at least one hardenable, solventless liquid, organometallicceramic precursor binder comprises at least one composition selectedfrom the group consisting of polysilazane, polyureasilazane,polythioureasilazane, and polysiloxane.
 7. The process of claim 4,wherein said at least one hardenable, liquid, organometallic, ceramicprecursor binder comprises alkenyl, alkynyl, epoxy, acrylate ormethacrylate groups.
 8. The process of claim 4, wherein said at leastone hardenable, liquid, organometallic, ceramic precursor comprisespolysilazane.
 9. The process of claim 4, wherein said at least onehardenable, liquid, organometallic, ceramic precursor binder comprisesat least one polyureasilazane.
 10. The process of claim 4, wherein saidat least one hardenable, liquid, organometallic, ceramic precursorbinder comprises at least one polysiloxane.
 11. The process of claim 4,wherein said at least one hardenable, liquid, organometallic, ceramicprecursor binder comprises titanium, zirconium, aluminum, or silicon.12. The process of claim 11, wherein said at least one hardenable,liquid, organometallic, ceramic precursor binder comprises silicon. 13.The process of claim 4, wherein said at least one hardenable, liquid,organometallic, ceramic precursor comprises oxygen or nitrogen.
 14. Theprocess of claim 4, wherein said at least one hardenable, liquid,organometallic, ceramic precursor binder comprises nitrogen.
 15. Theprocess of claim 4, wherein said at least one hardenable, liquid,organometallic, ceramic precursor binder comprises alkenyl groups. 16.The process of claim 15 wherein said alkenyl groups comprise vinylgroups.
 17. The process of claim 4, wherein said at least onehardenable, liquid, organometallic, ceramic precursor binder comprisesfrom about 0.1% to about 20% of said sand/binder mixture based on thetotal weight of said sand/binder mixture.
 18. The process of claim 17,wherein said at least one hardenable, liquid, organometallic, ceramicprecursor binder comprises from about 0.1 wt % to about 5 wt % of saidsand/binder mixture based on the total weight of said sand/bindermixture.
 19. The process of claim 18, wherein said at least onehardenable, liquid, organometallic, ceramic precursor binder comprisesfrom about 0.1 wt % to about 2 wt % of said sand/binder mixture based onthe total weight of said sand/binder mixture.
 20. The process of claim4, wherein said at least one hardenable, liquid, organometallic, ceramicprecursor binder is hardened through the application of at least one ofheat, UV irradiation, or laser energy.
 21. The process of claim 20,wherein said at least one hardenable, liquid, organometallic, ceramicprecursor binder is hardened through the application of heat.
 22. Theprocess of claim 21, wherein said at least one hardenable, liquid,organometallic, ceramic precursor binder further comprises at least onefree radical generator.
 23. The process of claim 22, wherein said atleast one free radical generator comprises at least one peroxide or atleast one azo compound.
 24. The process of claim 23, wherein said atleast one peroxide comprises dicumyl peroxide.